Balancer Sets

Three-wire direct-current distribution systems are usually energized from a two-wire generator connected to the two outside lines. The approximately balanced voltages between the outside lines and the middle line are maintained in some cases by a balancer set connected as shown in Fig. 29-5.

Fig. 29-5. Three-Wire System With Balancer Set

The balancer set consists of two identical shunt or compound direct-current machines with their shafts rigidly coupled together and with their armature circuits connected in series across the outside lines of the three-wire system. The middle wire of the system is connected to a point between the armatures of the two machines.

The series fields of the two machines are so connected that, when a current flows therein because of load unbalance, the machine on the more heavily loaded side becomes a cumulative-compound generator while the machine on the more lightly loaded side becomes a differential-compound motor. Because the balancing action is dependent on current difference in the two sides of the system, it is not necessary that voltage unbalance actually occur before the restoring action is available. When the load is balanced, the two units run as
motors in series without load. Very close voltage regulation is possible by this method of compounding. Balancer sets are made of such size as to compensate for load unbalance of 25 or less per cent of the full capacity of the main generator.